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Magnetic Probe Extensometer

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The iMagnetic Extensometer is used to monitor soil or rock settlement and heave in excavations, foundations, dams, and embankments, tunnels, shafts and sheet piles. Data from the extensometer indicate the depths at which settlement has occurred as well as the total amount of settlement.

The Magnetic Extensometer System is installed at locations where monitoring of settlement or heave is needed.

The Magnetic Extensometer System comprises a probe, a graduated tape on a reel and an access pipe along which magnetic targets are positioned. A datum or reference magnet is fixed to the bottom pipe. The probe design incorporates triple reed switches. As the probe moves along the access pipe, it detects the magnets by way of a reed-switch circuit closing. This causes a light to display and a buzzer to sound at the reel.

Product Features:

• Versatile system with a variety of magnetic targets to suit different applications
• Measures settlement and heave
• Oversized targets are available to use with inclinometer casing
• Magnetic extensometer probe is available with various tape lengths
• Access tube can be extended through fill material
• Gives audio and visual indication of magnetic targets

The access tubing is installed to the length required, by coupling together successive three-metre lengths. Magnetic targets are installed as needed along the tubing, to the required depth.

Measurements are taken by lowering the suspended probe down the access pipe and using the graduated tape to measure the distance from the top of the access pipe to each magnetic target.

By taking repeated probe measurements of each target over a period of time, this shows any displacement of the ground being measured. Changes in this distance relative to the datum magnet near the base of the pipe will reflect the rock and soil movements along the axis of the access casing

The bottom of the access pipe is anchored into stable ground such as bedrock. Any settlement or heave of the ground being measured will cause the magnets to move along the axis of the pipe. Various types of magnetic targets are available. There are three-legged and six-legged spider magnets, retained by leaf springs, for use in boreholes. Plate magnets are also available for placing in soil or fill when adding further sections of tubing during construction.

Product Benefits:

• Reliable and accurate measuring system that is easy to read
• Any number of targets can be monitored in a single borehole
• One probe reads at many locations; only the access tubing and magnet targets are permanently installed in the ground

Ordering Information:

Magnet Targets
For 33.4mm outer diameter access tube
E2-1.1-1 Datum magnet
E2-1.1-2 3 leaf spider magnet push in. For 65-120mm diameter bore
E2-1.1-4 3 leaf spider magnet push in. For 120-225mm diameter bore
E2-1.1-5 Plate mounted magnet
E2-1.1-6 6 leaf spider magnet. Mechanical Release, for 120-225mm diameter bore

Magnet Targets
For 70mm outer diameter inclinometer casing
E2-1.2-1 Datum magnet
E2-1.2-2 Plate mounted magnet
E2-1.2-3 6 leaf spider magnet. Mechanical Release, for 130-250mm diameter bore
E2-1.2-4 3 leaf spider magnet push in. For 150-200mm diameter bore
E2-1.2-5 3 leaf spider magnet push in. For 180-325mm diameter bore

Magnet Targets
For 85mm outer diameter inclinometer casing
E2-1.3-1 Datum magnet
E2-1.3-2 Plate mounted magnet
E2-1.3-3 6 leaf spider magnet. Mechanical Release, for 140-270mm diameter bore

Tubes And Fittings
E2-2.1-A Access tube, flush threaded 33.4mm outer diameter. 3 metre length
E7-2.11 Telescoping access tube 33.4mm outer diameter. Internal tube, 2 metre length.
E7-2.12 Telescoping Access Tube 48.5mm outer diameter. 2 metre length. 1No required per extension rod
E2-2.9 End cap. To fit 35mm outer diameter tubing
S17-4.2 End cap. To fit 50mm outer diameter tubing
E2-2.13 Protective cover. 2inch BSP Threaded cap. 50mm inner diameter, 500mm length.
E2-2.14 Security cover. With bar and padlock. 50mm inner diameter, 500mm length.